So i want to get the first DDL showing all distinct project ..which is done so far - I am looking to add a 2nd DDL that includes all distinct BU "departments"under same project ..

That sounds quite straight forward. All it would take is to loop through each of your projects collating the Distinct BU values, so you can sort them, and then update the second drop down (with show all as the first entry) with their names.

When one is chosen, the onchange event of that drop down is from where you would use the selected BU to update a selected view, if you have one there.